How to say in Czech: How good is their Serbian?

English
How good is
Czech
Jak dobře umějí srbsky?
Their Serbian is getting better.
Their Serbian is very good.
How do you say that in Serbian?
I do not speak Serbian very well.
You speak Serbian very well.
Their native language is Serbian.
Are they learning Serbian on their own?
He is learning Serbian.
He is not Serbian.
He is Serbian.

Czech phrasebook and translator with tens of thousands of sentences translated by humans. Czechslator is being developed by Michal Měchura. CREDITS Czechslator's sentence generation engine is partially based on Grammatical Framework. All Czech pronunciation is computer-generated using Microsoft Azure Text to Speech. When Czechslator cannot find a translation in its own database, it looks in the PanLex dictionary or obtains a machine translation from Microsoft Translator. PRIVACY Czechslator does not save any cookies in your web browser and does not collect personally identifiable data. Czechslator uses StatCounter for traffic analysis, configured not to save any cookies in your web browser and not to collect any personally identifiable data.